The term "swing stage" is used in the specification in the conventional sense of a suspended platform. Its principal structural component is referred to herein as a "swing stage base". Such a base is generally supported by a pair of stirrups and cables. In turn, the base supports flooring, workmen and equipment, and supports an enclosing structure such as a handrail assembly or mesh fastened to vertical posts. The base is the component most subject to mechanical stresses.
A swing stage base is commonly constructed of aluminum to reduce weight. The dominant design involves a ladder-like construction. The principal components are two parallel beams, each consisting of two horizontal box beams joined by vertical uprights. Horizontal cross-members join the lower box beams to form a unitary structure. The various components are hollow extruded members. The uprights and horizontal cross-members are retained in passages between opposing walls of the box beams. They are joined to the beams by swedging, constricting the member to enter one end of a passage and flaring the member at the opposite end to secure the junction. The equipment required to form such joints is comparatively expensive, but avoids any significant handworking of the basic aluminum materials. This is very desirable since aluminum components cannot be heated or repeatedly deformed in an elastic manner as readily as components formed of metals such as mild steel and cannot withstand comparable abue during hand-forming. It is also generally desirable to avoid hand-forming to whatever extent possible to reduce construction costs.
The prior ladder-like swing stages are difficult to transport. The enclosing structure generally poses no problem, usually being releasable from the base or knock-down. The vertical posts of the enclosing structure are often located in the interiors of the vertical uprights and can be readily removed. The principal problem is the construction of the swing stage base itself. This is a monolithic structure several feet wide and often up to thirty feet long. Transportation from the manufacturing site to a remote location, via train or truck, can be very costly. Even local transportation is difficult. Despite such limitations, the ladder-like swing stages still dominate the swing stage market.